1. Field of the Invention
The present invention generally relates to methods of reducing inflammation. More specifically, the invention relates to methods for reducing inflammation caused by proinflammatory cytokines or an inflammatory cytokine cascade.
2. Description of the Related Art
Vertebrates achieve internal homeostasis during infection or injury by balancing the activities of proinflammatory and anti-inflammatory pathways. However, in many disease conditions, this internal homeostasis becomes out of balance. For example, endotoxin (lipopolysaccharide, LPS) produced by all Gram-negative bacteria activates macrophages to release cytokines that are potentially lethal (44; 10; 47; 31).
Inflammation and other deleterious conditions (such as septic shock caused by endotoxin exposure) are often induced by proinflammatory cytokines, such as tumor necrosis factor (TNF; also known as TNF.alpha. or cachectin), interleukin (IL)-1.alpha., IL-1.beta., IL-6, IL-8, L-18, interferony, platelet-activating factor (PAF), macrophage migration inhibitory factor (MIF), and other compounds (42). Certain other compounds, for example high mobility group protein 1 (HMG-1), are induced during various conditions such as sepsis and can also serve as proinflammatory cytokines (57). These proinflammatory cytokines are produced by several different cell types, most importantly immune cells (for example monocytes, macrophages and neutrophils), but also non-immune cells such as fibroblasts, osteoblasts, smooth muscle cells, epithelial cells, and neurons (56). Proinflammatory cytokines contribute to various disorders, notably sepsis, through their release during an inflammatory cytokine cascade.
Inflammatory cytokine cascades contribute to deleterious characteristics, including inflammation and apoptosis (32), of numerous disorders. Included are disorders characterized by both localized and systemic reactions, including, without limitation, diseases involving the gastrointestinal tract and associated tissues (such as appendicitis, peptic, gastric and duodenal ulcers, peritonitis, pancreatitis, ulcerative, pseudomembranous, acute and ischemic colitis, diverticulitis, epiglottitis, achalasia, cholangitis, coeliac disease, cholecystitis, hepatitis, Crohn's disease, enteritis, and Whipple's disease); systemic or local inflammatory diseases and conditions (such as asthma, allergy, anaphylactic shock, immune complex disease, organ ischemia, reperfusion injury, organ necrosis, hay fever, sepsis, septicemia, endotoxic shock, cachexia, hyperpyrexia, eosinophilic granuloma, granulomatosis, and sarcoidosis); diseases involving the urogential system and associated tissues (such as septic abortion, epididymitis, vaginitis, prostatitis and urethritis); diseases involving the respiratory system and associated tissues (such as bronchitis, emphysema, rhinitis, cystic fibrosis, adult respiratory distress syndrome, pneumonitis, pneumoultramicroscopicsilicov-olcanoconiosis, alvealitis, bronchiolitis, pharyngitis, pleurisy, and sinusitis); diseases arising from infection by various viruses (such as influenza, respiratory syncytial virus, HIV, hepatitis B virus, hepatitis C virus and herpes), bacteria (such as disseminated bacteremia, Dengue fever), fungi (such as candidiasis) and protozoal and multicellular parasites (such as malaria, filariasis, amebiasis, and hydatid cysts); dermatological diseases and conditions of the skin (such as burns, dermatitis, dermatomyositis, sunburn, urticaria warts. and wheals); diseases involving the cardiovascular system and associated tissues (such as vasulitis, angiitis, endocarditis, arteritis, atherosclerosis, thrombophlebitis, pericarditis, myocarditis, myocardial ischemia, congestive heart failure, periarteritis nodosa, and rheumatic fever); diseases involving the central or peripheral nervous system and associated tissues (such as Alzheimer's disease, meningitis, encephalitis, multiple sclerosis, cerebral infarction, cerebral embolism, Guillame-Barre syndrome, neuritis, neuralgia, spinal cord injury, paralysis, and uveitis); diseases of the bones, joints, muscles and connective tissues (such as the various arthritides and arthralgias, osteomyelitis, fasciitis, Paget's disease, gout, periodontal disease, rheumatoid arthritis, and synovitis); other autoimmune and inflammatory disorders (such as myasthenia gravis, thryoiditis, systemic lupus erythematosus, Goodpasture's syndrome, Behcets's syndrome, allograft rejection, graft-versus-host disease, Type I diabetes, ankylosing spondylitis, Berger's disease, Type I diabetes, ankylosing spondylitis, Berger's disease, and Retier's syndrome); as well as various cancers, tumors and proliferative disorders (such as Hodgkins disease); and, in any case the inflammatory or immune host response to any primary disease (13; 55; 30; 20; 33; 25; 18; 27; 48; 24; 7; 9; 4; 3; 12; 8; 19; 15; 23; 49; 34).
Mammals respond to inflammation caused by inflammatory cytokine cascades in part through central nervous system regulation. This response has been characterized in detail with respect to systemic humoral response mechanisms during inflammatory responses to endotoxin (2; 54; 21; 28). In one set of responses, afferent vagus nerve fibers are activated by endotoxin or cytokines, stimulating the release of humoral anti-inflammatory responses through glucocorticoid hormone release (51; 41; 39). Previous work elucidated a role for vagus nerve signaling as a critical component in the afferent loop that modulates the adrenocorticotropin and fever responses to systemic endotoxemia and cytokinemia (14; 11; 52; 35). However, comparatively little is known about the role of efferent neural pathways that can modulate inflammation.
Efferent vagus nerve signaling has been implicated in facilitating lymphocyte release from thymus via a nicotinic acetylcholine receptor response (1). Clinical studies have also indicated that nicotine administration can be effective for treating some cases of inflammatory bowel disease (17; 36), and that proinflammatory cytokine levels are significantly decreased in the colonic mucosa of smokers with inflammatory bowel disease (40). However, none of these findings would suggest that cholinergic agonists can inhibit an inflammatory cytokine cascade, particularly those mediated by macrophages. Also, there is no suggestion in the literature that efferent vagus nerve stimulation is effective in inhibiting these cascades.